Thalamic activation during an attention-to-prepulse startle modification paradigm: A functional MRI study

Background: Prepulse inhibition (PPI) of the startle reflex reflects early stages of information processing and is modulated by selective attention. A nimal models indicate medial frontal-thalamic circuitry is important in PPI modulation. We report data from the first functional magnetic resonance im aging (fMRI) study examining whether attending to or ignoring a prepulse di fferentially activates brain areas within this circuitry. Methods: Ten healthy subjects received structural and functional MRL During fMRI acquisition, subjects heard intermixed attended and ignored tones ser ving as prepulses to the startle stimulus. Regions of interest were traced on structural MR1 and coregistered to fMRI images. Results: Greater amplitude fMRI blood-oxygen-level-dependent response to at tended than ignored PPI conditions occurred in the right thalamus, and bila terally in the anterior and mediodorsal thalamic nuclei, whereas the startl e-alone condition showed deactivation. In transitional medial cortex (Brodm ann Area 32), which is involved in affective processing of noxious stimuli, the startle-alone condition elicited the greatest response, the attended-P PI condition showed the smallest response, and the ignored-PP1 condition wa s intermediate. Conclusions: These findings extend animal models to humans by indicating th alamic involvement in the modulation of PPI. Further fMRI investigations ma y elucidate other kev structures in the circuitry underlying normal and dis ordered modulation of PPL (C) 2001 Society of Biological Psychiatry.